Rotary position indicator and control station



ROTARY POSITION INDICATOR AND-CONTROL STATION Filed Sept. 10, 1964 H. H.FLUM July 23, 1968 5 Sheets-Sheet 2 nvvavro HERMAN H FLU/M H. H. FLUM3,394,292

ROTARY POSITION INDICATOR AND CONTROL STATION Jul 23, 1968 5Sheets-Sheet 5 Filed Sept. 10, 1964 E 6 6 i l R UC$ W m R PAL WTA E am Dmw w 9% Fear; mp5

lNVENTOR' HERMAN 6'. F1. (/44 BY FROM K E) PROCESB ELEMENT A 77'OR/VE Y33%,292 Patented July 23, 1968 3,394,292 ROTARY POSITION INDICATOR ANDCONTROL STATION Herman H. Flum, Woodland Hills, Los Angeles, Calif.,

assignor to The Bunker-Ramo Corporation, Canoga Park, Calif., acorporation of Delaware Filed Sept. 10, 1964, Ser. No. 395,446

13 Claims. (Cl. 318-18) ABSTRACT OF THE DISCLOSURE An apparatus isdisclosed in which the rotary position of a first element is displayedand controlled. The first element is coupled to a second element whichrotates in response to signals from a source, such as a computer. A pairof limiters, which are selectively positionable, are included to limitthe rotary motion of the first element to be within a range, defined bythe limiters positions, by the engagement of a dial which is mounted onthe first element with either of the two limiters. The station alsoincludes means to bias either or both of the limiters to enable the dialto bypass them and thereby permit unimpeded rotary motion of the firstelement.

This invention relates to a system for producing analog output signalsin response to manually or automatically supplied input signals. Moreparticularly, the invention relates to a novel set point station whichproduces, in response to input signals from a process control computer,output signals for use in the control process. The novel set pointstation is also adapted to produce output signals in response to manualcontrols.

Since the development of high speed computing devices such as digitalcomputers, the number of industrial processes that are controlled bysuch devices has constantly increased. Basically, a digital computerused for process control is connected to key subsystems or elements ofthe instrumentation or equipment wherein the process takes place. Eachof such key elements generally includes transducing means for producingsignals related to various physical conditions or forces therein. Thesesignals are supplied as input signals to the computer, which ispreprogrammed with instructions for controlling the process so as tooptimize its performance. The computer, on the basis of the inputsignals and the pre-programmed instructions, computes the desiredphysical conditions or forces which should be present or take place ineach of the process elemnts. On the basis of the computations, thecomputer supplies related signals for each of the key elements in orderto control that phase of the process occurring therein.

In practice, a process control digital computer does not supply signalsdirectly to the key elements. Rather, it supplies the signals tointermediary devices known as set point stations, each of which convertsthe signals supplied thereto into related analog output signals for useby each key element in the process. In order to provide safe boundariesof performance, each set point station is provided with limiting deviceswhich prevent the station from producing analog output signals beyondpredetermined limits, irrespective of the magnitude of the input signalsfrom the computer. Such limiting devices insure that the key processelements will not be subjected to physical conditions or forces beyondthose which are expected and regarded as safe in the process whenoperating under normal conditions. In addition, it is often desirablethat each set point station produce output signals under manual control,so that an operator may be able to set the set point station to producea desired output signal to control the key element of. the processassociated therewith. Being able to manually control the process isespecially desirable either when initiating the process, or, while theprocess is being controlled by the computer, it is desired to vary thephysical conditions or forces in the key element so as to furtheroptimize or control the process. For complete flexibility in manuallycontrolling the station, it is desirable to be able to cause the stationto produce output signals even beyond the limits determined by thelimiting devices associated therewith. Such flexibility enables thecomputer to control the key elements even beyond the limits by adjustingthe parameters of the process so that eventually the physical conditionsor forces occurring in each key element are again within thepro-selected limits of operation.

The present invention provides a computer controlled set point stationwhich possesses all of the previously described advantages, and inaddition provides other desirable features which contribute to theproper control of each key element of the process. The set point stationof the present invention also includes visual indication means so thatan operator may visual-1y be informed at all times of the state ofoperation of the station. For example, the indicating means may indicatethat signals are supplied from the computer, as well as indicate thecharacteristics of the output signals supplied from the set pointstation to the process element with which it is interconnected.

The present invention is based on utilizing input signals, such as maybe supplied by a process control computer, to control the energizationof a reversible motor which controls the rotation of an output member.The position of the output member is in turn used to produce outputsignals which are analogous to the input signals supplied from thecomputer. The rotation of the output member is selectively mechanicallylimited to a preselected range of rotation, thereby limiting the outputsignals produced as a function of the position thereof from exceedingpredetermined values.

In addition, the invention provides mechanical mean-s for bypassing themechanical limitations placed on the rotation of the output member sothat the output signals produced by the set point station are notrestricted or limited, and if an operator so desires, can still bedirectly related to the input signals supplied from the process controlcomputer. The set point station disclosed herein fur ther includesmanual controls so that an operator may, irrespective of the inputsignals from the computer, manually vary the output signals supplied bythe set point station to a key element in the process with which it isassociated. Mechanical and electrical switching means are also providedto prevent input signals from the computer from energizing thereversible motor when the set point station is set to operate only in amanual mode of operation.

The front panel of the set point station is provided with a dial havinga plurality of markings thereon. The markings enable an operator tovisually observe the characteristics or magnitude of the output signalas indicated by an output indicator as well as the relative positions ofthe mechanical limiters which may be physically positioned with respectto pre-selected markings of the dial. A plurality of light indicatorsare also provided on the front panel for visually determining variousconditions of the operation of the set point station. For example,indicator lights are provided to indicate the direction of rotation ofthe reversible motor, namely, whether the motor is being driven in anupscale direction, or whether it is being driven in a downscaledirection. An indicator light is also provided to indicate that theoutput signal has reached one of the preselected limiting values whichoccurs when the output indicator is physically constrained from furtherrotation by one of the mechanical limiters. In addition, the set pointstation disclosed herein provides for a plurality of signals, indicativeof various conditions of Operation therein, to be fed back to thecomputer. Thus, the computer constantly monitors the efiect of thesignals supplied by it to the set point station as well as the exactoperating condition of the station. For example, the computer may besupplied with a limits bypassed feedback signal indicating that theoutput signal that the set point station may produce is not limited bythe mechanical limiters described hereinbefore. Similarly, the computermay be supplied wit-h an at-limits feedback signal whenever the outputindicator is physically or mechanically restricted by the mechanicallimiters from further rotation. The computer may also be supplied with amode-control feedback signal which indicates whether the station isunder computer control, or whether the output signal which the stationproduces is only a function of manual operation.

The novel features which are believed to be characteristic of theinvention, together with further objects and advantages thereof, will bebetter understood from the fol lowing description taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a block diagram of an embodiment of the invention;

FIGURE 2 is a front view of a portion of the apparatus of the inventionshowing most of the mechanically interconnect-ed elements thereof;

FIGURE 3 is a top view of a portion of the elements shown in FIGURE 2;

FIGURE 4 is a schematic diagram of a portion of the present invention;and

FIGURE 5 is an isometric view of the front panel of the set pointstation of the invention.

Reference is now made to FIGURE 1 wherein a reversible motor 21 is shownmechanically coupled to a gear assembly 22 through a clutch 23. Thereversible motor is adapted to be energized by signals supplied from aprocess control computer by means of a pair of lines. One line is acommon power line 25 which supplies the signals to the reversible motor21 through serially connected mode control switch 27 and normally-closedlimits bypass switch 28. The other line by which the signals aresupplied to the reversible motor 21 may be either a line 31 or a line32, depending on whether the motor is to be driven so as to producerotational motion in a first direction, hereinafter also referred to asthe upscale direction, or whether the motor is to be driven in a seconddirection opposite to the first direction, hereinafter also referred toas the downscale direction. The gear assembly 22 is mechanically coupledto an output gear 33 which is in turn coupled to an output indicator orpointer 35. The output gear 33 and the output indicator 35 rotate as afunction of the rotational motion produced by the reversible motor 21.The magnitude of notation as well as the direction of rotation of theoutput gear 33 and the output indicator 35 are directly related to thesignals supplied to the reversible motor from the process controlcomputer. The output gear 33 may be coupled to an electrical outputmeans 37 so that the output thereof is made to be directly proportionalto the magnitude and direction of rotation of the output gear 33.Similarly, the output gear 33 may be connected through arotational-to-linear motion converter 38 to a pneumatic transmitter 39,so that the pneumatic output of the transmitter is made to be directlyproportional to the direction and magnitude of rotation of the outputgear 33. The conversion of the magnitude and direction of rotation of amember such as the output gear 33 into proportional electrical pneumaticsignals is well known in the art and therefore its detailed descriptionis deemed unnecessary.

As previously stated, signals from the computer are supplied to thereversible motor 21 by means of the line 25 through the mode controlswitch 27 and the limits bypass switch 28. The mode control switch 27may be a single pole switch which may be positioned in either a computersetting or a manual setting. The signals from the computer can pass tothe reversible motor 21 through the mode control switch 27 only when thelatter switch is in the computer setting. Similarly, the signals fromthe computer to the reversible motor 21 can pass the limits bypassswitch 23 only when the switch is de-energized, that is, when the switchcontacts are closed. However, if the mode control switch 27 is in themanual setting previously referred to and/or the limits bypass switch 28is energized by a mechanical limits bypass means 41 to which its iscoupled, as will be explained later in greater detail, the signals fromthe computer to the reversible motor 21 are interrupted, therebypreventing the reversible motor 21 from producing rotational motion andaffecting the position of the output gear 33.

Assume that the mode control switch 27 is in the computer settingpreviously referred to, and that the limits bypass switch 28 isde-energized so that signals from the computer may pass by means of theline 25 to the reversible motor 21. Further assume that the signals aresupplied to the reversible motor by means of the line 31 so that thereversible motor is caused to rotate in an upscale direction. Thereversible motor 21 may be of the type which produces rotational motionas a function of the duration of the signals supplied thereto; that is,it produces rotational motion for the time duration that pulses orsignals are supplied thereto. On the other hand, the reversible motor 21may be of the type which responds to the number of pulses supplied toit, rather than to their time duration. Such a motor is analogous to astepping motor, stepping or rotating by a predetermined amount for eachpulse supplied thereto. The present invention is adapted to use eithertype of motor, the only requisite being that the signals supplied to thereversible motor from the computer produce rotational motion ofpredetermined magnitude and direction as a function thereof.

From the foregoing description, it is apparent that as long as signalsare supplied to the reversible motor 21 from the computer through thelines 25 and 31, the motor 21 will rotate in the upscale direction,thereby causing the output gear 33 and the output indicator 35 to rotatein the upscale direction by an amount which is a function of either theduration of the signals from the computer or the number of the pulsestherefrom, depending on what type of reversible motor is being used. Forexplanatory purposes only, hereinafter the reversible motor 21 will bedescribed as having a pair of windings which, when alternatelyenergized, cause the motor to rotate in 0pposite directions. The motoris supplied with signals of volts of alternating current (A.C.) 60cycles per second (cps), of varying time duration, so that the amount ofrotational motion produced by the motor 21 is a function of the durationof the 110 volt, 60 c.p.s. signals supplied to it.

As previously explained, it is generally desired that each set pointstation be provided with limiting devices for preventing the stationfrom automatically producing analog output signals beyond predeterminedamplitude limits. This prevents the key process element which isassociated with the set point station from being subjected to physicalforces or conditions beyond those expected or desired in normal processoperations. Such limiting devices are provided in the present invention,as seen from FIGURE 1, wherein a high limiter 43 and a low limiter 44are shown. The high and low limiters are mechanical members which may bepositioned at predetermined positions in the path of the outputindicator 35 so that it cannot bypass the position of either the highlimiter 43 or the low limiter 44. Since the output indicator 35 isdirectly coupled to the output gear 33, by limiting the motion of theoutput indicator 35, the high and low limiters 43 and 44, respectively,limit the freedom of rotation of the output gear 33 to a range ofrotation corresponding to the distance between the posi tions at whichthe two mechanical members are positioned. As a consequence, the outputsignals produced in response to the position or rotation of the outputgear 33 are thereby limited to be Within a preselected range. The highlimiter 43 and the low limiter 44 have limit switches 45 and 46,respectively coupled thereto. The limit switches 45 and 46 are energizedonly when the output indicator 35 is in physical contact with either ofthe limiters with which the switches are associated. When energized,either of the limit switches 45 or 46 energizes a limit light indicator47, thereby providing visual indication to an operator that the outputindicator has reached either the high limiter 43 or the low limiter 44.This indicates that the output signal of the set point station is eitherat the high or low boundary or limit of the range of output signals thatthe set point station is to produce.

As seen from FIGURE 1, the present invention further provides a manualcontrol 49 which is mechanically coupled to the gear assembly 22. Thisprovides manual control of the rotational position of the gear assembly22 and the rotational position of the output gear 33, irrespective ofthe rotational motion produced by the reversible motor 21 in response tosignals supplied from the process control computer. For completeflexibility in the production of output signals which the set pointstation of the present invention may provide, the invention disclosedherein further provides a mechanical limit bypass means 41 which isadapted to mechanically prevent the high limiter 43 and low limiter 44from restricting the motion of the output indicator 35. The mechanicallimit bypass means 41 biases the limiters 43 and 44 in such a mannerthat the motion of the output indicator 35 is no longer restricted. As aconsequence, the position of the output gear 33, which is coupled to theindicator 35, is a function only of the rotational motion produced bythe reversible motor 21 or of any rotational motion that is produced bythe manual control 49.

For a more complete mechanical description of the station of theinvention, reference is made to FIGURE 2, wherein the reversible motor21 is shown coupled through its shaft 21a and gears 21b and 210 to theclutch 23. The clutch is coupled to the gear assembly 22 through a shaft22a on which gears 22b and 210 are mounted. The output gear 33, which isshown coupled to the gear assembly 22 by means of the gear 22b, is alsoconnected to the output indicator 35 by means of a common shaft 33a. InFIGURE 2, the electrical output means 37 is shown in the form of apotentiometer 37a coupled to the output gear 33 by a potentiometer gear37b so that the position of the sliding arm (not shown) of thepotentiometer is a function of the rotation of the output gear 33. Therotational-to-linear motion converter 38 previously referred to is shownin FIGURE 2 in block form coupled to the shaft 33a of the output gear33. The converter 38 detects the rotational motion of the output gear 33and converts it to linear motion for producing proportionate pneumaticoutput signals. The manual control 49 is shown in FIGURE 2 as comprisinga thumb wheel 49 which is coupled to the shaft 22a of the gear assembly22 through a pair of pulleys 49a and 49c, intercoupled by a string orbelt 4%.

From FIGURE 2, it is apparent that the rotation of the output gear 33 isa function of the rotational motion produced by the motor 21. Forexample, if the motor shaft 21a is rotated in a clockwise direction, asindicated by an arrow CW, it is seen that the gear 21b is rotated in aclockwise direction, causing gears 21c and 22b to turn in acounterclockwise direction (CCW). The latter gear causes the output gear33 to turn in a direction opposite thereto, namely, in a clockwisedirection. The magnitude of rotation of the gear 33 caused by therotation of the motor shaft 21a is a function of all the gearsintercoupling the two, but the direction of rotation of the output gear33 is directly related to the direction of rotation of the shaft 21a.Since the output indicator 35 is directly coupled to the output gear 33by means of the shaft 33a, both the magnitude and direction of rotationthereof are directly related to that of the output gear 33.

Refernce is now made to FIGURE 3, wherein the output gear 33 and theoutput indicator 35 coupled thereto are shown rotating or turning in aclockwise direction as indicated by the arrow CW. The output indicatoris shown having a pointer or front portion 35 and a pin 35p verticallydisposed with respect to the longitudinal axis of the pointer. In FIGURE3, the high limiter 43 and the low limiter 44 having pointers or frontportions 43 and 44 respectively, are also shown. The low limiter 44 isphysically positioned or fixed with respect to the plate or housing ofthe set point station by means of a fastening screw 44s. The limiter 43is similarly fastened to the plate or housing by a fastening screw (notshown). The limiters 43 and 44 have opposing notches 43n and 4421,respectively, the size of the notches being sufficient for the pin 35pof the output indicator 35 to be engaged therein when the outputindicator 35 is rotated so that it physically engages either of thelimiters. For example, if the output indicator 35 continues to turn in aclockwise direction from the position shown in FIGURE 3, it willeventually reach the position of the low limiter 44. Thereafter it willbe prevented from continuing its clockwise rotation by the pin 35p beingengaged in the notch 4411 whose position is fixed with respect to thehousing. Once the rotation of the output indicator is restricted, it isreflected back by restricting the rotation of the output gear 33 and thegear assembly 22 which then becomes decoupled from the motor 21 by meansof the slip clutch 23. The restriction of rotation of the output gear 33in a clockwise direction results in a proportional limitation on theoutput signal that may be produced in response to the position thereof.

From FIGURES 2 and 3, it is apparent that even though the motor shaft2.1a may continue to rotate in a clockwise direction, once the outputindicator 35 is physically restrained by the limiter 44, the clockwiserotation of the armature 21 will not affect the position of the outputgear 33. However, if the signals supplied to the motor 21 cause themotor to rotate in a counterclockwise direction, the output gear 33 willrespond thereto and will cause the output indicator 35 to becomephysically disengaged from the limiter 44. If, however, the rotationalmotion in a counterclockwise direction continues until the pin 35pengages the notch 4311 of the high limiter 43, the counter clockwiserotation of the output indicator will cease. Thus, the engagement of thepointer 35 limits the rotation of the output gear 33 and as aconsequence limits the output signal which is produced as a function ofthe rotation thereof. In practice, the low limiter 44 and the highlimiter 43 are positioned so as to enable the output gear to rotate onlyin a predetermined range which is directly related to the desired rangeof output signals. So long as the output indicator 35 is between the twolimiters, the output signals are directly controlled by the signals fromthe process control computer. However, as soon as the output indicatoris physically or mechanically limited by either of the limiters fromfreely rotating, the output signal does not exceed the value establishedby the position of the limiter irrespective of additional signals thatthe computer may supply. Such an output signal limiting arrangement ismost significant since it prevents the set point :station from producingoutput signals beyond predetermined limits, irrespective of the signalsfrom the process control computer. This prevents abnormal or undesiredsignals from being supplied to any key element which responds to suchoutput signals.

Under some circumstances, however, it may be desired to bypass thelimiters so that the output signals of the set point station are notrestricted to be within any limiting values. The present inventionprovides the mechanical limits bypass means 411 (FIGURES 1, 2 and 3)which, as seen from FIGURE 2, may be turned in a clockwise directionabout a pivot 41a to a bias position as indicated by the dashed lines.When turned to the bias position, the mechanical'limits bypass means 41biases the output indicator 35 away from the limiters 43 and 44 so thatthe pin 35p cannot engage either of the notches 43n and 4411 (FIGURE 3).Alternatively, the limiters 43 and 44 may be physically biased away fromthe output indicator 35 in order to prevent the pin 35;) thereof fromengaging notches 43n or 4411. In either case, however, by turning thebypass means 41 to the bias position the rotation of the outputindicator is no longer restricted by the limiters 43 and 44.

The position of the mechanical limits bypass means 41 controls thelimits bypass switch 28 so that, when the mechanical bypass means 41 isturned to its bias position, the switch 28 is energized; that is, itsnormally closed contacts are opened. As a result, the signals from theprocess control computer can no longer energize the reversible motor 21as explained in conjunction with FIGURE 1. It is apparent, therefore,that whenever the limits established by the limiters 43 and 44 arebypassed, the motor 21 is disconnected from the computer if the bypassmeans 41 is left in its bias position.

The mechanical limits bypass means 41 may be temporarily moved to itsbias position so as to permit the output indicator to move to a positionoutside the range between the two limiters, then the bypass means 41 maybe returned to its normal position. It is apparent from the foregoingdescription that once the output in dicator is outside the range definedby the two limiters, its movement is no longer restricted. Under suchcircumstances, the computer may control the rotational mo tion of theoutput indicator in either direction, since the notches 43m and 4411(FIGURE 3) only restrict the output indicator from getting out of therange between the limiters. However, once the output indicator isoutside the range between the limiters, the computer may control theposition of the output indicator and cause it to re-enter the limitedrange. For example, in the set point station disclosed herein as shownin FIGURE 3, the output indicator may be temporarily biased and rotatedclockwise beyond the limiter 44. Then the indicator may be unbiased. Insuch a case, the computer will control the rotation of the outputindicator in either direction. The rotation in a clockwise direction isunrestricted since the limiter 44 has already been manually bypassed.Rotation in a counter-clockwise direction is similarly unrestrictedsince the notch 4412 of the limiter 44 only engages the pin 35p when theoutput indicator is turning in a clockwise direction. Thus the computermay cause the output indicator to re-enter the range between thelimiters 43 and 44. Such an arrangement is most significant since it mayoften be desired not to change the settings of the limiters and yet beable to produce output signals beyond the limits established by thelimiters. Likewise, it may be desirable to permit the computer tocontinuously control the magnitude of the output signals supplied to thekey element of the process with which the set point station isinterconnected.

As previously explained in connection with FIGURE 1, the limiters 43 and44 have limit switches 45 and 46, respectively, coupled thereto. Theswitches 45 and 46 are positioned adjacent notches 4312 and 4411,respectively. They are activated by the pin 35;) of the output indicator35 whenever the output indicator is in physical contact with theirrespective limiter. Whenever either the switch 45 or the switch46 isactivated or energized, a limit light indicator 47 (FIGURE 1) isenergized, thereby providing a visual indication that the rotation ofthe output indicator 35 is physically restricted by either the highlimiter 43 or the low limiter 44.

The set point station of the invention disclosed herein may furthercomprise additional light indicators for visual indication of variousphenomena occurring therein. For example, as shown in FIGURE 1, the setpoint station includes an upscale light indicator 51 which is coupled tothe signal line 31. The indicator 51 is energized only when thereversible motor 21 produces rotational motion in the upscale directionin response to signals supplied via the line 31. Similarly, a downscalelight indicator 52, which is coupled to the signal line 32, is energizedonly when the motor 21 produces rotational motion in the downscaledirection in response to signals supplied via the line 32. The set pointstation further includes a computer-limits light indicator 54 which isconnected to the junction of the limits bypass switch 28 and the motor21. The indicator 54 is energized only when signal from the processcontrol computer may be supplied to the motor via the line 25 which, aspreviously explained, can occur only if the mode control switch 27 is inthe computer setting and the limits bypass switch 28 is deenergized.

In addition to providing visual indication of the occurrence of variousconditions in the station, the invention provides means for feeding backsignals to the computer from key points in the station, so that thecomputer not only supplies the set point station with input signalswhich cause the motor 21 to produce rotational motion in either of twodirections, but the computer also monitors the conditions produced oroccurring therein.

Reference is now made to FIGURE 4 wherein the elements of the set pointstation of the present invention which produce or respond to electricalsignals are schematically diagrammed. As seen therein, the reversiblemotor 21 includes windings 21a and 21d which are connected to the lines31 and 32, respectively, the junction point of the windings beingconnected to the line 25 through the switches 28 and 27. From FIGURE 4,it is seen that power signals can be supplied to the motor 21 via theline 25 only when the switch 27 is in the computer setting and theswitch 28 is in its de-energized, normally-closed state as shown.However, even if the two switches (27 and 28) are in a state as shown inFIGURE 4, whether winding 21u or winding 21d is energized to cause themotor to produce rotational motion in an upscale direction or adownscale direction, respectively, depends on whether the signals aresupplied on line 31 or line 32. The winding 21a is shunted by theupscale light indicator 51 so that only when the winding 21a isenergized, causing the motor to produce rotational motion in the upscaledirection, is the indicator 51 energized or illuminated. Similarly, thedownscale light indicator 52 connected across the windings 21d is onlyenergized when the winding 21d is energized so as to produce rotationalmotion in the downscale direction. The computer-limits light indicator54 is connected to the line 25 through a current limiting resistor 54rand the switches 28 and 27, the other terminal of the indicator 54 beingconnected to a second power line P. It is apparent that the indicator 54will be energized by current through the lines P and 25 only when theswitches 27 and 28 are in the state shown in FIGURE 4, namely, the modecontrol switch 27 is in the computer setting and the limit bypass switch28 is deenergized.

The limit switches 45 and 46 (see FIGURES 1 and 2) are connected inparallel between the lines 25 and P through serially connected limitlight indicator 47 and a current limiting resistor 47r. The indicator 47is energized only if one of the switches 45 and 46 is closed to providea continuous electrical path between the lines 25 and P. From theforegoing description, this occurs only when the pin 35p of the outputindicator 35 is engaged in either of the notches 4312 or 4411 of thelimiters 43 and 44, respectively. It is apparent, therefore, that thelimit light indicator 47 is energized or illuminated only when theoutput indicator 35 is physically restricted by either of the limiters43 and 44.

As previously stated, the set point station of the present invention mayfurther comprise means for feeding back signals indicative of conditionsin the station to the process control computer, so that the computer mayconstantly monitor the state of operation thereof. For example, the factthat the output indicator 35 is physically restricted by either of thelimiters from freely rotating may be fed back to the computer byproviding the limit switches 45 and 46 with additional cont-acts 45a and46a which are serially connected between leads 61 and 62 irom thecomputer. As long as neither of the limit switches 45 and 46 isactuated, the contacts 45a and 46a will remain in their closed states sothat they provide a continuous path between the leads 61 and 62.However, as soon as either of the limit switches 45 or 46 is actuated,its respective contacts 45a or 46a open to interrupt the continuous pathbetween the leads 61 and 62, thereby indicating to the computer that theoutput indicator 35 is at one of the limits.

By employing similar circuit design techniques, the fact that the outputindicator 35 is physically biased by the mechanical limits bypass means41 (FIGURES 2 and 3) may be indicated to the computer. For example, thelimits bypass switch 28 associated with the bypass means 41 for biasingthe output indicator may be provided with additional contacts 28a whichare connected between leads 65 and 66 from the computer. As long as theswitch 28 is unactuated, namely, when the output indicator is notphysically biased, the contacts 28a provide an open path between theleads 65 and 66. However, as soon as the switch 28 is actuated, due tothe bypass means 41 biasing the output indicator, the contacts 28a closeto provide a continuous path between the leads 65 and 66 which is sensedby the process control computer. Similarly, the setting of the modecontrol switch 27 may be indicated to the computer by providingadditional contacts 27a coupled to the switch 27 and connected on oneside to the lead 65 through the contacts 28a, the other side of contacts27a being connected to a lead 67. As seen from FIGURE 4, a continuouspath between the leads 65 and 67 exists only if the contacts 28a are intheir normally closed state (when the output indicator is not:physically biased) and the mode control switch 27 and contacts 27a arein the computer mode setting as shown. A change in state of either thecontacts 27a and 28a will interrupt the path between the leads 65 and67, thereby indicating to the computer that either the station is in themanual mode of operation and/or that the limiters 43 and 44 have beenphysically bypassed.

The set point station of the present invention may further include adevice such as an indicating meter 70 which is coupled by means of leads68 and 69 to the key element of the process to which the stationsupplies its output signals. Such a meter 70 may provide visualindication at the set point station of the actual state of conditions orforces generated in the key element.

Reference is now made to FIGURE wherein a front panel 100 of the setpoint station disclosed herein is shown in an isometric view. As seentherefrom, the mode control switch 27 as well as the upscale lightindicator 51, the downsoale light indicator 52, the limit lightindicator 47 and the computer limits light indicator 54 are mounted onthe bottom half of the panel 100. .A dial 90 having markings thereon isalso mounted in the panel 100. The range of markings on thedial is, ofcourse, related to the maximum range of the output signals that thestation may produce. As seen from FIGURE 5, the pointers 44 35 and 43 ofthe low limiter 44, the output indicator 35 and the high limiter 43,respectively, are also seen through the front panel 100. The limiters 44and 43 are positioned by means of their respective positioning screws44s and 43s (see FIGURE 3). Thus, the pointers 44f and 43 are positiondwith respect to the markings of the dial 90 which relate to the lowerand upper limits, respectively, of the desired range of output signals.Such an arrangement enables an operator to observe at all times themagnitude of the output signal, as indicated by the position of thepointer 35f with respect to the markings of the dial 90, as well asnotice the limits imposed on such an output signal. The mechanicallimits bypass means 41 previously described is not positioned on thefront panel 100. Rather, it is mounted in a less accessible place on theside of the station to insure that an operator does not inadvertentlycause it to bias the output indicator and thereby enable the station toprovide output signals beyond a range which is deemed safe.

A portion of the thumb wheel 49 of the manual control 49 (FIGURE 2) isalso exposed through the front panel so that an operator may manuallycontrol the magnitude of the output signals. A set point station whichalso includes the meter 70 whose function was previously explained mayhave the meter mounted on the front panel. By viewing only the frontpanel an operator may thus be visually apprised of the operating stateof the station as well as particular conditions occurring therein, andthe effect of the output signals supplied to the key element of theprocess with which the station is interconnected.

From the foregoing description, it becomes apparent that the presentinvention provides a versatile set point station which may provideoutput signals in response to automatically supplied input signals.Limits may be placed on the output signals so that only signals within apredetermined range can be produced. In addition, means are provided forbypassing the limits without altering their position so that theautomatically supplied signals may cause the set point station toprovide output signals which are only limited by the particular meansused to produce the output signals.

The set point station of the invention provides a significant degree offlexibility in that even when the station is operated in the computermode of operation with limits imposed on the output signals, an operatormay manually bypass the output indicator 35 over either of the limiters43 or 44 and then permit the computer to control the production ofoutput signals even beyond the limited range. However, once the outputindicator rotates into a position between the two limiters, the outputsignals are again restricted to the preselected limited range of outputsignals. For example, assuming that the output indicator 35 shown inFIGURE 3 rotates in a clockwise direction, from the foregoingdescription it is apparent that once the output indicator 35 ismechanically limited by the limiter 44 the clockwise rotation thereof isrestricted. However, by mechanically biasing the output indicator 35, itmay continue to rotate clockwise beyond the limiter 44. Furthermore, thecomputer may control the output indicator to also turn in acounterclockwise direction and re-enter the range between the twolimiters 43 and 44 since the notches 4311 and 44n only engage the pin3512 in order to limit the output indicator from rotating beyond therange defined by their position but do not prevent the output indicatorfrom reentering the range therebetween.

It is understood that many changes and modifications may be made by oneskilled in the art without departing from the true spirit and scope ofthe invention.

I claim:

1. A set point station comprising:

first means for producing rotary motion in either of two oppositedirections in response to signals supplied thereto from a source ofsignals;

second means including a rotatable output member coupled to said firstmeans whereby said rotatable output member rotates as a function of therotary motion produced by said first means;

an output indicator coupled to said rotatable output member and adaptedto be rotated therewith;

at least one limiter for mechanically limiting said output indicator andsaid second means from rotating in at least a first direction beyond apredetermined point;

manual control means coupled to said second means for manually rotatingsaid rotatable output member; mode control means for interrupting theresponse of said first means to said signals supplied from said sourceso! that said rotatable output member is rotatable only by manuallyoperating said manual control means; and

output means coupled to said rotatable output member for producing anoutput signal as a function of the position thereof.

2. A set point station comprising:

first means for producing rotary motion in either of two oppositedirections in response to signals supplied thereto from a source ofsignals;

second means including a rotatable output member coupled to said firstmeans whereby said rotatable output member rotates as a function of therotary motion produced by said first means;

an output indicator coupled to said rotatable output member and adaptedto be rotated therewith;

at least one limiter for mechanically limiting said output indicator andsaid second means from rotating in at least a first direction beyond apredetermined point;

limit bypassing means actuatable to mechanically permit said outputindicator to bypass said at least one limiter so as to prevent said atleast one limiter from mechanically limiting the rotation of said outputindicator; and

output means coupled to said rotatable output member for producing anoutput signal as a function of the position thereof.

3. The set point station defined by claim 2 further including electricallimits bypassing switching means responsive to actuation of said limitsbypassing means for interrupting the response of said first means tosaid signals supplied from said source of signals.

4. A set point station comprising:

first means including a reversible motor responisve to input signalssupplied thereto from a source of signals for rotating in either of twoopposite directions as a function of said input signals;

second means including clutch means and an ou put member coupled throughsaid clutch means to said motor for rotating said output member as afunction of the rotation of said motor;

an output indicator coupled to said output member to be rotatedtherewith;

a dial having a plurality of visual markings thereon for indicating therelative position of said output indicator with respect thereto;

first and second limiters positioned with respect to preselectedmarkings on said dial for mechanically limiting the rotation of saidoutput indicator and said output member so that the position of saidoutput member with respect to said dial is limited to the range betweenthe preselected markings with respect to which said first and secondlimiters are positioned;

limit bypassing means actuatable to mechanically permit said outputindicator to bypass said first and second limiters so as to prevent saidlimiters from mechanically limiting the rotation of said output memberand said output indicator;

manual control means coupled to said second means for manually rotatingsaid output member in either of said two opposite directions; and

output means responsive to the rotational position of said output memberfor producing an output signal related thereto.

5. The set point station defined by claim 4 further including:

first and second electrical limit contact means coupled to said firstand second limiters, respectively whereby said first electrical limitcontact means is mechanically actuated when the rotation of said outputindicator is mechanically limited by said first limiter and said secondelectrical limit contact means is mechanically actuated when therotation of said output indicator is mechanically limited by said secondlimiter.

6. The set point station defined by claim 5 further including? limitindicator means for indicating that either of said first electricallimit contact means or said second electrical limit contact means isactuated.

7. The set point station defined by claim 5 further including:

limit feedback means coupled to said first and second electrical limitcontact means for supplying a limit output signal whenever said firstelectrical limit contact means or said second electrical limit contactmeans is actuated.

8. The set point station defined by claim 4 further including:

first and second indicating means coupled to said reversible motor, saidfirst indicating means being energized when said reversible motor isrotating in a first direction of said two opposite directions and saidsecond indicating means being energized when said reversible motor isrotating in a second direction of said two opposite directions.

9. The set point station defined by claim 4 further including:

mode control means adapted to be set in either a manual mode or sourcemode setting for interrupting the supply of input signals to saidreversible motor when set in said manual mode setting so that saidoutput member is rotatable only by manually operating said manualcontrol means.

10. The set point station defined by claim 9 further including:

mode feedback means coupled to said mode control means for producing afeedback signal indicative of the setting of said mode control means.

11. The set point station defined by claim 9 further including:

electrical limits bypassing switching means responsive to actuation ofsaid limits bypassing means for interrupting the supply of said inputsignals to said first means.

12. The set point station defined b-y claim 11 further including:

limit feedback means coupled to said electrical limits bypassingswitching means for producing a feedback signal indicative of whethersaid electrical limits bypassing switching means is actuated by saidlimits bypassing means.

13. The set point station defined by claim 11 further including:

a source limits indicator for indicating that said mode control means isin said source mode setting and that said electrical limits bypassingswitching means is not actuated by said limits bypassing means so thatthe supply of said input signals from said source to said reversiblemotor is not interrupted.

References Cited UNITED STATES PATENTS BENJAMIN DOBECK, PrimaryExaminer.

